The goal of a video teleconferencing system is to bring teleconferencing participants as "close together" as possible. Ideally, the effect obtained in a good teleconferencing system should be one of "being there".
The traditional video teleconference facility puts extreme limitations on the normal human protocols for interaction. Most traditional teleconference facilities offer some version of NTSC video which is displayed on a small-sized, home-television-like monitor. When the number of teleconference participants at the sending end of a conference is larger than one, the image of each participant occupies a small portion of an already small viewing area. As a result, it becomes difficult for viewers at the receiving end of such a teleconference to pick up non-verbal cues from a speaker's face and body. Indeed, in many cases, it is often difficult to discern at the receiving end who of the many participants at the sending end is actually talking.
To overcome this problem, it is desirable for a video teleconferencing facility to replace the conventional monitor with a larger monitor which provides a wide aspect ratio, panoramic view of the remote teleconferencing site. An ordinary NTSC monitor is relatively square, having an aspect ratio which is four units in the horizontal direction to three units in the vertical direction (i.e., 4.times.3=1.33.times.1). Because of this, it is not desirable to simply replace the conventional small-sized teleconference monitor with a large-sized monitor having the same NTSC aspect ratio. The reason is that in many cases a plurality of teleconference participants at a remote site sit side-by-side. When an image of the remote site is locally displayed on an NTSC monitor of any size, good interaction with the participants at the remote site is not achieved, as the relatively square aspect ratio of the NTSC monitor does not permit a wide enough view of the remote conference site. Accordingly, it is desirable to replace the small-sized NTSC monitor of the conventional teleconference facility with a monitor having a wide aspect ratio screen, specifically, a screen with a wider aspect ratio than the conventional NTSC monitor.
One way to achieve a wide aspect ratio display for a teleconferencing facility is to utilize High Definition Television (HDTV) equipment. An HDTV monitor has an aspect ratio of 16.times.9 (1.78.times.1) which is wider than the NTSC aspect ratio of 4.times.3 (1.33.times.1). Unfortunately, the high cost and large transmission bandwidth (approximately 622 Mbp/s for digital transmission and 30 MHz for analog transmission) and the requirement for large lighting levels at the conference sites make presently available HDTV equipment unsuitable for most teleconferencing applications.
Another approach for achieving a teleconferencing system with wide aspect ratio displays is to equip each teleconference station with a plurality of NTSC video cameras, each generating an NTSC video signal corresponding to a sub-image. For example, two NTSC cameras can be positioned so that their fields of view are side by side. Each of the cameras produces a sub-image which by its itself has a 4.times.3 aspect ratio. The individual sub-images are each transmitted via an individual transmission channel to a remote teleconference site. At the remote teleconference site, multiple projectors are aligned to display the sub-images on a screen in a side-by-side fashion. The net result is a combined image having a wide aspect ratio of 8.times.3.
There are several problems associated with the use of a plurality of NTSC cameras to produce a single wide aspect ratio video image. One problem is that the multiple cameras cannot simply be placed side by side. Such an arrangement of cameras results in a complicated overlapping of the fields of view of the individual cameras so that there are some spatial locations which are in the field of view of no camera and some spatial locations which are in the field of view of more than one camera. To overcome this problem, sophisticated optical and/or electronic arrangements may be utilized to insure that the fields of view of the multiple cameras merge continuously into a single field of view (see U.S. Pat. No. 4,890,314). Similarly, the multiple projectors at the display end must be precisely positioned so that the individually displayed sub-images merge to form a single combined image. Thus, this approach to wide aspect ratio video teleconferencing requires precision mechanical alignments which are vulnerable to slight physical perturbations of either the cameras or the projectors. The net result is a fragile system requiring frequent maintenance. Multiple cameras and projectors also have the tendency to exhibit color and image size variations causing distortions in the merged sub-images. With multiple cameras, projectors and transmission channels, the overall system becomes expensive to own and operate.
In view of the foregoing, it is an object of the present invention to provide a video teleconferencing system, utilizing a wide aspect ratio display at each teleconferencing site, which overcomes the shortcomings of the prior art systems. In particular, it is an object of the present invention to provide a teleconferencing system which provides a wide aspect ratio display at each site utilizing a single NTSC camera and projector at each site.